This invention relates to an apparatus for the discrimination of myoelectric potential patterns, to be used in a drive mechanism which is controlled by using, as instruction signals, various myoelectric potentials issuing from a given part of the human body.
The external-prosthesis, which aims to give relief to persons disabled by the absence of or defect in their body parts, is most advanced in the field of artificial legs and artificial arms. Artificial arms, in particular, are required to produce complicated motions. Drive mechanisms developed for operating such artificial arms by effective use of electric motors and hydraulic drive means have reached a high degree of perfection. The control of a drive mechanism, however, calls for highly complicated processing. Various methods have heretofore been proposed for the purpose of this control. Unfortunately, these methods tend to entail the common disadvantage that the control devices which embody their respective principles are unproportionately large in size for the number of modes of motions the artificial arms are expected to produce. Different methods have also been proposed for the discrimination of control signals used for causing artificial arms to produce motions. One of these methods involves use of a plurality of independent input devices and another utilizes prescribed voice sounds uttered by the user as instruction signals. All of these conventional methods are deficient, in varying measures, of the ability to provide artificial arms with perfect control devices fully satisfactory for actual use.
For a disabled person to enjoy the smoothest natural use of an artificial arm for example, the prime and sole requisite is that the entire control system should be amply small and light and it should enable the muscles in certain relevant part of the subject, such as his shoulder or remaining brachium, to issue instruction signals to the drive mechanism for the artificial arm in entirely the same manner as the above mentioned relevant part would do in moving a natural arm. The best way to fulfill this requisite resides in limiting the number of modes of motions of the artificial arm to the irreducible minimum and thereby decreasing the size and weight of the device to the fullest possible extent and using, as instruction signals for the control device, the myoelectric potentials (hereinafter referred to as "EMG") issued by the muscles of the relevant part of the subject in moving his natural arm.
Such instruction signals are effectively extracted from the muscles of the relevant part of the subject by attaching a plurality of electrodes for extracting EMG signals to as many positions around the relevant region and converting the EMG signals generated in the relevant region into a corresponding EMG pattern by means of the aforementioned extraction electrodes. Where such an EMG pattern is used as an instruction signal, a plurality of EMG patterns are generally classified on a basis of the linear discriminant principle. Methods proposed heretofore are invariably based on a principle that the control of an artificial arm is accomplished by prescribing a definite number of modes of motions the artificial arm is expeced to produce, fixing discriminant functions one each for the aforementioned different modes of motions, and providing the same number of circuits adapted to perform arithmetic operations on the discriminant functions as that of modes of motions, whereby the circuit, upon receiving incoming EMG signals, will carry out arithmetic operations on corresponding discriminant functions, compare the results of these operations with one another and single out the largest value which determines the exact motion to be imparted to the artificial arm. Devices embodying such conventional methods are required to incorporate as many circuits as there are modes of motions and, therefore, tend to make up much space. Since the discrimination devices heretofore known to the art mostly depend for the aforementioned processing of arithmetic functions upon general-purpose computers, their hardware structures take up too much space to be applied advantageously to artificial limbs.
An object of this invention, therefore, is to provide a compact apparatus for the discrimination of EMG patterns for use in a drive mechanism adapted to impart motions to an artificial limb, which apparatus extracts EMG signals issuing from a given part of a disabled person and uses them as instruction signals for the control of the drive mechanism, performs arithmetic operations on the corresponding discriminant functions at high speed and enables the artificial arm to produce smooth natural motions faithfully in response to the results of the operations.